The present invention relates to an anchor bolt and more particularly to an anchor bolt for fixing various members such as an angle bar etc. to a wall of a structure made of concrete, for example.
A prior art for the anchor bolt has been disclosed in U.S. Pat. No. 3,937,119 (U.S. Pat. Ser. No. 535,536 Dec. 23, 1974).
The anchor bolt of this prior art has a head portion and a shank which is provided with a pair of threads consisting of a guide thread and a tapping thread. The crest diameter of the guide thread is set almost equal to the inside diameter of a bore provided in a structural body. The crest diameter of the tapping thread is set larger than the inside diameter of the bore. The tapping thread is provided with a plurality of notches.
When this anchor bolt is screwed into the bore, the guide thread smoothly leads the shank without causing the axis of the shank to shift from the screwing direction, and an amount of material is broken off by the notches of the tapping thread from the structural body and filled into the space around the root of thread so that the shank is firmly embedded in the structural body.
The superiority of the anchor bolt in the above prior art stems from the idea of filling the space between the anchor bolt and the inner surface of the bore with the amount of material broken off by the notches. However, it is not so pull-out resistant to being pulled out after it is embeding as was intended.
In the arrangement of this prior art, both the root portions of the guide thread and the tapping thread are so much smaller in diameter compared to the inside diameter of the bore that large spaces are formed between each of the root portions of the threads and the inside wall of the bore. Accordingly, it is not possible for these spaces to be completely and tightly charged with particles of the material. Additionally, in this prior art, as the flanks of the crest of the tapping thread has flanks configure a pair of equal legs in a section thereof, it is understood that the arrangement has been made without consideration of the strength of the screw thread and consequent improvement in the resistance to being pulled out.